Preservation and Authenticity of the Holy Quran
1. Prophet Muhammad (pbuh) himself supervised and authenticated the written texts of the Qur’an
Whenever the Prophet received a revelation, he would first memorize it himself and later declare the revelation and instruct his Companions (R.A. – Radhi Allahu Taala Anhu) – May Allah be pleased with him who would also memorize it. The Prophet would immediately ask the scribes to write down the revelation he had received, and he would reconfirm and recheck it himself. Prophet Muhammad (pbuh) was an Ummi who could not read and write. Therefore, after receiving each revelation, he would repeat it to his Companions. They would write down the revelation, and he would recheck by asking them to read what they had written. If there was any mistake, the Prophet would immediately point it out and have it corrected and rechecked. Similarly he would even recheck and authenticate the portions of the Qur’an memorized by the Companions. In this way, the complete Qur’an was written down under the personal supervision of the prophet (pbuh).
2. Order and sequence of Qur’an divinely inspired
The complete Qur’an was revealed over a period of 22½ years portion by portion, as and when it was required. The Qur’an was not compiled by the Prophet in the chronological order of revelation. The order and sequence of the Qur’an too was Divinely inspired and was instructed to the Prophet by Allah (swt) through archangel Jibraeel. Whenever a revelation was conveyed to his companions, the Prophet would also mention in which surah (chapter) and after which ayat (verse) this new revelation should fit.
Every Ramadhaan all the portions of the Qur’an that had been revealed, including the order of the verses, were revised and reconfirmed by the Prophet with archangel Jibraeel. During the last Ramadhaan, before the demise of the Prophet, the Qur’an was rechecked and reconfirmed twice.
It is therefore clearly evident that the Qur’an was compiled and authenticated by the Prophet himself during his lifetime, both in the written form as well as in the memory of several of his Companions.
3. Qur’an copied on one common material
The complete Qur’an, along with the correct sequence of the verses, was present during the time of the Prophet (pbuh). The verses however, were written on separate pieces, scrapes of leather, thin flat stones, leaflets, palm branches, shoulder blades, etc. After the demise of the prophet, Abu Bakr (r.a.), the first caliph of Islam ordered that the Qur’an be copied from the various different materials on to a common material and place, which was in the shape of sheets. These were tied with strings so that nothing of the compilation was lost.
4. Usman (r.a.) made copies of the Qur’an from the original manuscript
Many Companions of the Prophet used to write down the revelation of the Qur’an on their own whenever they heard it from the lips of the Prophet. However what they wrote was not personally verified by the Prophet and thus could contain mistakes. All the verses revealed to the Prophet may not have been heard personally by all the Companions. There were high possibilities of different portions of the Qur’an being missed by different Companions. This gave rise to disputes among Muslims regarding the different contents of the Qur’an during the period of the third Caliph Usman (r.a.).
Usman (r.a.) borrowed the original manuscript of the Qur’an, which was authorized by the beloved Prophet (pbuh), from Hafsha (may Allah be pleased with her), the Prophet’s wife. Usman (r.a.) ordered four Companions who were among the scribes who wrote the Qur’an when the Prophet dictated it, led by Zaid bin Thabit (r.a.) to rewrite the script in several perfect copies. These were sent by Usman (r.a.) to the main centres of Muslims.
There were other personal collections of the portions of the Qur’an that people had with them. These might have been incomplete and with mistakes. Usman (r.a.) only appealed to the people to destroy all these copies which did not match the original manuscript of the Qur’an in order to preserve the original text of the Qur’an. Two such copies of the copied text of the original Qur’an authenticated by the Prophet are present to this day, one at the museum in Tashkent in erstwhile Soviet Union and the other at the Topkapi Museum in Istanbul, Turkey.
5. Diacritical marks were added for non-Arabs
The original manuscript of the Qur’an does not have the signs indicating the vowels in Arabic script. These vowels are known as tashkil, zabar, zair, paish in Urdu and as fatah, damma and qasra in Arabic. The Arabs did not require the vowel signs and diacritical marks for correct pronunciation of the Qur’an since it was their mother tongue. For Muslims of non-Arab origin, however, it was difficult to recite the Qur’an correctly without the vowels. These marks were introduced into the Quranic script during the time of the fifth ‘Umayyad’ Caliph, Malik-ar-Marwan (66-86 Hijri/685-705 C.E.) and during the governorship of Al-Hajaj in Iraq.
Some people argue that the present copy of the Qur’an that we have along with the vowels and the diacritical marks is not the same original Qur’an that was present at the Prophet’s time. But they fail to realize that the word ‘Qur’an’ means a recitation. Therefore, the preservation of the recitation of the Qur’an is important, irrespective of whether the script is different or whether it contains vowels. If the pronunciation and the Arabic is the same, naturally, the meaning remains the same too.
6. Allah Himself has promised to guard the Qur’an
Allah has promised in the Qur’an :
"We have, without doubt, sent down the Message; and We will assuredly Guard it (from corruption). [Al-Qur’an 15:9]
Source :
http://www.islam101.com/quran/preservedQ.htm
(peace and blessings of Allaah be upon him). 
